Method for performing random access at adaptive transmission point in wireless communication system that uses mmWave band

ABSTRACT

Provided is a method for performing random access, the method comprising: obtaining information associated with a phase pattern vector set and information associated with a sequence set to be used during a random access process; selecting one phase pattern vector corresponding to the number of repetitive transmissions of an RACH signal, among a plurality of phase pattern vectors included in the phase pattern vector set; transmitting, to a base station, an RACH signal during a time section corresponding to the number of repetitive transmissions of an RACH signal, at a predetermined transmission point in the entire time section corresponding to the maximum number of repetitive transmissions; and receiving, from the base station, an RACH response signal indicating an estimated sequence, an estimated phase pattern vector, and an estimated transmission point.

This application is a National Stage Application of InternationalApplication No. PCT/KR2016/005317, filed on May 19, 2016, which claimsthe benefit of U.S. Provisional Application No. 62/167,902, filed on May29, 2015, all of which are hereby incorporated by reference in theirentirety for all purposes as if fully set forth herein.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of performing a random access by a userequipment at an adaptive transmission timing in a wireless LAN systemusing an mmWave band.

BACKGROUND ART

An ultrahigh frequency wireless communication system based on mmWave isconfigured to operate at a center frequency of several GHz to severaltens of GHz. Due to such a characteristic of the center frequency, in ammWave communication system, a pathloss may appear noticeably in a radioshadow area. Considering such a pathloss, it is necessary to improve arandom access procedure between a user equipment (UE) and a base station(BS). Moreover, in case that a plurality of user equipments exist, it isnecessary to design a random access procedure by considering possibilityof potential collision between RACH (random access channel) signals.

DISCLOSURE OF THE INVENTION Technical Task

The present invention is directed to solve the above problems of thegeneral technology, and one technical task of the present invention isto establish a stable connection by improving a random access procedurebetween a base station and a user equipment in a wireless communicationsystem.

Another technical task of the present invention is to resolve RACHsignal collision between user equipments by adaptively adjusting atransmission timing for performing a random access.

Further technical task of the present invention is to configure a phasepattern vector set for a random access, thereby enabling a base stationto perform a random access procedure without interference despite adynamic transmission timing change.

The technical problems solved by the present invention are not limitedto the above technical problems and other technical problems which arenot described herein will become apparent to those skilled in the artfrom the following description.

Technical Solutions

In one technical aspect of the present invention, provided herein is amethod of performing a random access, including obtaining information ona sequence set and a phase pattern vector set to use for an randomaccess procedure, selecting a prescribed phase pattern vectorcorresponding to a repetitive transmission count of an RACH (randomaccess channel) signal from a plurality of phase pattern vectorsincluded in the phase pattern vector set, sending the RACH signalgenerated using a prescribed sequence selected from a plurality ofsequences included in the sequence set and the selected phase patternvector to a base station for a time interval amounting to the repetitivetransmission count at a specific transmission timing in a whole timeinterval corresponding to a maximum repetitive transmission count, andreceiving an RACH response signal indicating an estimated sequence, anestimated phase pattern vector and an estimated transmission timing fromthe base station.

A phase pattern vector set corresponding to a specific repetition countmay be configured with usable phase pattern vectors only among all phasepattern vectors orthogonal to each other.

The usable phase pattern vectors may be determined to satisfy relationof being nested orthogonal to phase pattern vectors configuring a phasepattern vector set corresponding to a different repetition count.

If the maximum repetitive transmission count is 8, the specifictransmission timing may correspond to a 0^(th) OFDM (orthogonalfrequency division multiplexing) symbol. If the maximum repetitivetransmission count is 4, the specific transmission timing may correspondto the 0^(th) OFDM symbol or a 4^(th) OFDM symbol. If the maximumrepetitive transmission count is 2, the specific transmission timing maycorrespond to the 0^(th) OFDM symbol, a 2^(nd) OFDM symbol, the 4^(th)OFDM symbol, or a 6^(th) OFDM symbol.

The estimated sequence, the estimated phase pattern vector and theestimated transmission timing may be determined according to a sequence,phase pattern vector and repetition count that maximize a correlationvalue with the RACH signal sent by the user equipment.

If a service radius of the base station increases, the number of phasepattern vectors configuring a phase pattern vector set of a bigrepetition count may be defined to increase and the number of phasepattern vectors configuring a phase pattern vector set of a smallrepetition count may be defined to decrease.

In another technical aspect of the present invention, provided herein isa user equipment, including a transmitting unit, a receiving unit, and aprocessor configured to operate by being connected to the transmittingunit and the receiving unit, wherein the processor is further configuredto obtain information on a sequence set and a phase pattern vector setto use for an random access procedure, select a prescribed phase patternvector corresponding to a repetitive transmission count of an RACH(random access channel) signal from a plurality of phase pattern vectorsincluded in the phase pattern vector set, control the transmitting unitto send the RACH signal generated using a prescribed sequence selectedfrom a plurality of sequences included in the sequence set and theselected phase pattern vector to a base station for a time intervalamounting to the repetitive transmission count at a specifictransmission timing in a whole time interval corresponding to a maximumrepetitive transmission count, and control the receiving unit to receivean RACH response signal indicating an estimated sequence, an estimatedphase pattern vector and an estimated transmission timing from the basestation.

Advantageous Effects

According to embodiments of the present invention, the following effectsare expected.

First of all, as a random access procedure between a base station and auser equipment in a wireless communication system is improved, RACHsignal collision of user equipments can be resolved.

Secondly, as a random access procedure can be improved by a process fordifferentiating a configuration of a phase pattern vector only,implementation complexity demanded for a base station is minimized.

Thirdly, an RACH procedure between user equipments respectively havingdifferent repetitive transmission counts can be performed withoutcollision with interference.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinmay be derived by those skilled in the art from the followingdescription of the embodiments of the present invention. That is,effects which are not intended by the present invention may be derivedby those skilled in the art from the embodiments of the presentinvention.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. The technical features of the present invention are notlimited to specific drawings and the features shown in the drawings arecombined to construct a new embodiment. Reference numerals of thedrawings mean structural elements.

FIG. 1 is a diagram illustrating a Doppler spectrum.

FIG. 2 is a diagram illustrating narrow beamforming related to thepresent invention.

FIG. 3 is a diagram illustrating a Doppler spectrum when narrowbeamforming is performed.

FIG. 4 is a diagram showing an example of a synchronization signalservice area of a base station.

FIG. 5 shows an example of a frame structure proposed in a communicationenvironment that uses mmWave.

FIG. 6 shows a structure of OVSF (orthogonal variable spreading factor)code.

FIG. 7 is a diagram to describe a disposed situation of user equipments.

FIG. 8 is a diagram to describe a method of performing a random accessprocedure according to one embodiment.

FIG. 9 is a flowchart showing a method of performing a random accessprocedure according to one embodiment.

FIG. 10 is a flowchart showing a repetition count determining methodaccording to another embodiment.

FIG. 11 is a diagram to describe a method of performing a random accessprocedure according to another embodiment.

FIG. 12 is a diagram to describe a method of performing a random accessprocedure according to another embodiment.

FIG. 13 is a diagram to describe a method of performing a random accessprocedure according to further embodiment.

FIG. 14 is a diagram showing a configuration of a user equipment and abase station related to a proposed embodiment.

BEST MODE FOR INVENTION

Although the terms used in the present invention are selected fromgenerally known and used terms, terms used herein may be varieddepending on operator's intention or customs in the art, appearance ofnew technology, or the like. In addition, some of the terms mentioned inthe description of the present invention have been selected by theapplicant at his or her discretion, the detailed meanings of which aredescribed in relevant parts of the description herein. Furthermore, itis required that the present invention is understood, not simply by theactual terms used but by the meanings of each term lying within.

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered optional factors on the conditionthat there is no additional remark. If required, the individualconstituent components or characteristics may not be combined with othercomponents or characteristics. In addition, some constituent componentsand/or characteristics may be combined to implement the embodiments ofthe present invention. The order of operations to be disclosed in theembodiments of the present invention may be changed. Some components orcharacteristics of any embodiment may also be included in otherembodiments, or may be replaced with those of the other embodiments asnecessary.

In describing the present invention, if it is determined that thedetailed description of a related known function or construction rendersthe scope of the present invention unnecessarily ambiguous, the detaileddescription thereof will be omitted.

In the entire specification, when a certain portion “comprises orincludes” a certain component, this indicates that the other componentsare not excluded and may be further included unless specially describedotherwise. The terms “unit”, “-or/er” and “module” described in thespecification indicate a unit for processing at least one function oroperation, which may be implemented by hardware, software or acombination thereof. The words “a or an”, “one”, “the” and words relatedthereto may be used to include both a singular expression and a pluralexpression unless the context describing the present invention(particularly, the context of the following claims) clearly indicatesotherwise.

In this document, the embodiments of the present invention have beendescribed centering on a data transmission and reception relationshipbetween a mobile station and a base station. The base station may mean aterminal node of a network which directly performs communication with amobile station. In this document, a specific operation described asperformed by the base station may be performed by an upper node of thebase station.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a base station, various operations performed forcommunication with a mobile station may be performed by the basestation, or network nodes other than the base station. The term basestation may be replaced with the terms fixed station, Node B, eNode B(eNB), advanced base station (ABS), access point, etc.

The term mobile station (MS) may be replaced with user equipment (UE),subscriber station (SS), mobile subscriber station (MSS), mobileterminal, advanced mobile station (AMS), terminal, etc.

A transmitter refers to a fixed and/or mobile node for transmitting adata or voice service and a receiver refers to a fixed and/or mobilenode for receiving a data or voice service. Accordingly, in uplink, amobile station becomes a transmitter and a base station becomes areceiver. Similarly, in downlink transmission, a mobile station becomesa receiver and a base station becomes a transmitter.

Communication of a device with a “cell” may mean that the devicetransmit and receive a signal to and from a base station of the cell.That is, although a device substantially transmits and receives a signalto a specific base station, for convenience of description, anexpression “transmission and reception of a signal to and from a cellformed by the specific base station” may be used. Similarly, the term“macro cell” and/or “small cell” may mean not only specific coverage butalso a “macro base station supporting the macro cell” and/or a “smallcell base station supporting the small cell”.

The embodiments of the present invention can be supported by thestandard documents disclosed in any one of wireless access systems, suchas an IEEE 802.xx system, a 3rd Generation Partnership Project (3GPP)system, a 3GPP Long Term Evolution (LTE) system, and a 3GPP2 system.That is, the steps or portions, which are not described in order to makethe technical spirit of the present invention clear, may be supported bythe above documents.

In addition, all the terms disclosed in the present document may bedescribed by the above standard documents. In particular, theembodiments of the present invention may be supported by at least one ofP802.16-2004, P802.16e-2005, P802.16.1, P802.16p and P802.16.1bdocuments, which are the standard documents of the IEEE 802.16 system.

Hereinafter, the preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings. It is to beunderstood that the detailed description which will be disclosed alongwith the accompanying drawings is intended to describe the exemplaryembodiments of the present invention, and is not intended to describe aunique embodiment which the present invention can be carried out.

It should be noted that specific terms disclosed in the presentinvention are proposed for convenience of description and betterunderstanding of the present invention, and the use of these specificterms may be changed to another format within the technical scope orspirit of the present invention.

1. Communication System Using Ultrahigh Frequency Band

In an LTE (Long Term Evolution)/LTE-A (LTE Advanced) system, an errorvalue of oscillators between a UE and an eNB is defined by requirementsas follows.

UE Side Frequency Error (in TS 36.101)

The UE modulated carrier frequency shall be accurate to within ±0.1 PPMobserved over a period of one time slot (0.5 ms) compared to the carrierfrequency received from the E-UTRA Node B

eNB Side Frequency Error (in TS 36.104)

Frequency error is the measure of the difference between the actual BStransmit frequency and the assigned frequency.

Meanwhile, oscillator accuracy according to types of BS is as listed inTable 1 below.

TABLE 1 BS class Accuracy Wide Area BS ±0.05 ppm Local Area BS  ±0.1 ppmHome BS ±0.25 ppm

Therefore, a maximum difference in oscillators between a BS and a UE is±0.1 ppm, and when an error occurs in one direction, an offset value ofmaximum 0.2 ppm may occur. This offset value is converted to a unit ofHz suitable for each center frequency by being multiplied by the centerfrequency.

Meanwhile, in an OFDM system, a CFO value is varied depending on asubcarrier spacing. Generally, the OFDM system of which subcarrierspacing is sufficiently great is relatively less affected by even agreat CFO value. Therefore, an actual CFO value (absolute value) needsto be expressed as a relative value that affects the OFDM system. Thiswill be referred to as normalized CFO. The normalized CFO is expressedas a value obtained by dividing the CFO value by the subcarrier spacing.The following Table 2 illustrates CFO of an error value of each centerfrequency and oscillator and normalized CFO.

TABLE 2 Center frequency Oscillator Offset (subcarrier spacing) ±0.05ppm ±0.1 ppm ±10 ppm ±20 ppm  2 GHz (15 kHz) ±100 Hz ±200 Hz  ±20 kHz ±40 kHz (±0.0067) (±0.0133) (±1.3)  (±2.7) 30 GHz (104.25 kHz)  ±1.5kHz  ±3 kHz ±300 kHz ±600 kHz (±0.014) (±0.029) (±2.9)  (±5.8) 60 GHz(104.25 kHz)  ±3 kHz  ±6 kHz ±600 kHz  ±1.2 MHz (±0.029) (±0.058) (±5.8)(±11.5)

In Table 2, it is assumed that a subcarrier spacing is 15 kHz when thecenter frequency is 2 GHz (for example, LTE Rel-8/9/10). When the centerfrequency is 30 GHz or 60 GHz, a subcarrier spacing of 104.25 kHz isused, whereby throughput degradation is avoided considering Dopplereffect for each center frequency. The above Table 2 is a simple example,and it will be apparent that another subcarrier spacing may be used forthe center frequency.

Meanwhile, Doppler spread occurs significantly in a state that a UEmoves at high speed or moves at a high frequency band. Doppler spreadcauses spread in a frequency domain, whereby distortion of a receivedsignal is generated in view of the receiver. Doppler spread may beexpressed as f_(doppler)=(v/λ)cos θ. At this time, v is a moving speedof the UE, and λ means a wavelength of a center frequency of a radiowave which is transmitted. θ means an angle between the radio wave and amoving direction of the UE. Hereinafter, description will be given onthe assumption that θ is 0.

At this time, a coherence time is inverse proportion to Doppler spread.If the coherence time is defined as a time spacing of which correlationvalue of a channel response in a time domain is 50% or more, thecoherence time is expressed as

$T_{c} \approx {\frac{9}{16\pi\; f_{doppler}}.}$In the wireless communication system, the following Equation 1 whichindicates a geometric mean between an equation for Doppler spread and anequation for the coherence time is used mainly.

$\begin{matrix}{T_{c} = {\sqrt{\frac{9}{16\pi\; f_{doppler}}} = \frac{0.423}{f_{doppler}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

FIG. 1 is a diagram illustrating a Doppler spectrum.

A Doppler spectrum or Doppler power spectrum density, which indicates achange of a Doppler value according to a frequency change, may havevarious shapes depending on a communication environment. Generally, inan environment, such as downtown area, where scattering occursfrequently, if received signals are received at the same power in alldirections, the Doppler spectrum is indicated in the form of U-shape asshown in FIG. 1. FIG. 1 shows a U-shaped Doppler spectrum when thecenter frequency is f_(c) and a maximum Doppler spread value is f_(d).

FIG. 2 is a diagram illustrating narrow beamforming related to thepresent invention, and FIG. 3 is a diagram illustrating a Dopplerspectrum when narrow beamforming is performed.

In the ultrahigh frequency wireless communication system, since thecenter frequency is located at a very high band, a size of an antenna issmall and an antenna array comprised of a plurality of antennas may beinstalled in a small space. This characteristic enables pin-pointbeamforming, pencil beamforming, narrow beamforming, or sharpbeamforming, which is based on several tens of antennas to severalhundreds of antennas. This narrow beamforming means that a receivedsignal is received at a certain angle only not a constant direction.

FIG. 2(a) illustrates that a Doppler spectrum is represented in the formof U-shape depending on a signal received in a constant direction, andFIG. 2(b) illustrates that narrow beamforming based on a plurality ofantennas is performed.

As described above, if narrow beamforming is performed, the Dopplerspectrum is represented to be narrower than U-shape due to reducedangular spread. As shown in FIG. 3, it is noted from the Dopplerspectrum when narrow beamforming is performed that Doppler spread isgenerated at a certain band only.

The aforementioned wireless communication system using the ultrahighfrequency band operates on a band having a center frequency ranging fromseveral GHz to several tens of GHz. The characteristics of such a centerfrequency further worsen Doppler Effect generated from migration of auser equipment or influence of CFO due to an oscillator differencebetween a transmitter and a receiver.

FIG. 4 is a diagram showing an example of a synchronization signalservice area of a base station.

A user equipment (hereinafter abbreviated UE) performs synchronizationwith a base station using a downlink (DL) synchronization signaltransmitted by the base station. In such a synchronization process,timing and frequency are synchronized between the base station and theUE. In order to enable UEs in a specific cell to receive and use asynchronization signal in a synchronization process, the base stationtransmits the synchronization signal by configuring a beam width as wideas possible.

Meanwhile, in case of an mmWave communication system that uses a highfrequency band, a path loss in synchronization signal transmissionappears greater than that of a case of using a low frequency band.Namely, a system using a high frequency band has a supportable cellradius reduced more than that of a related art cellular system (e.g.,LTE/LTE-A) using a relatively low frequency band (e.g., 6 GHz or less).

As a method for solving the reduction of the cell radius, asynchronization signal transmitting method using a beamforming may beused. Although a cell radius increases in case of using a beamforming, abeam width is reduced disadvantageously. Equation 2 shows variation of areceived signal SINR according to a beam width.W→M ⁻² WSINR→M ²SINR  [Formula 2]

If a beam width is reduced by M⁻² time according to a beamforming,Equation 2 indicates that a received SINR is improved by M² times.

Beside such a beamforming scheme, as another method for solving the cellradius reduction, it is able to consider a scheme of transmitting a samesynchronization signal repeatedly. In case of such a scheme, although anaddition resource allocation is necessary or a time axis, a cell radiuscan be advantageously increased without a decrease of a beam width.

Meanwhile, a base station allocates a resource to each UE by schedulinga frequency resource and a time resource located in a specific section.In the following, such a specific section shall be defined as a sector.In the sector shown in FIG. 4, A1, A2, A3 and A4 indicate sectors havingwidths of 0˜15′, 15˜30′, 30˜45′ and 45˜60′ in radius of 0˜200 m,respectively. B1, B2, B3 and B4 indicate sectors having widths of 0˜15′,15˜30′, 30˜45′ and 45˜60′ in radius of 200˜500 m, respectively. Based onthe substance shown in FIG. 4, sector 1 is defined as {A1, A2, A3, A4}and sector 2 is defined as {A1, A2, A3, A4, B1, B2, B3, B4}. Moreover,if a current synchronization signal service area of a base station isthe sector 1, in order for the base station to service a synchronizationsignal for the sector 2, assume that an additional power over 6 dB isrequired for a transmission of a synchronization signal.

First of all, in order to service the sector 2, the base station canobtain an additional gain of 6 dB using a beamforming scheme. Throughsuch a beamforming process, a service radius can be extended from A1 toB1. Yet, since a beam width is reduced through the beamforming, A2 to A3cannot be serviced simultaneously. Hence, when a beamforming isperformed, a synchronization signal should be sent to each of the A2˜B2,A3˜B3, and A4˜B4 sectors separately. So to speak, in order to servicethe sector 2, the base station should transmit the synchronizationsignal by performing the beamforming four times.

On the other hand, considering the aforementioned repetitivetransmission of the synchronization signal, the base station may be ableto transmit the synchronization signal to the whole sector 2. Yet, thesynchronization signal should transmit the synchronization signal on atime axis repeatedly four times. Consequently, a resource necessary toservice the sector 2 is identical for both a beamforming scheme and arepetitive transmission scheme.

Yet, since a beam width is narrow in case of to beamforming scheme, a UEmoving fast or a UE located on a sector boundary has difficulty inreceiving a synchronization signal stably. Instead, if an ID of a UElocated beam is identifiable, a UE can advantageously grasp its locationthrough a synchronization signal. On the contrary, since a beam width iswide in case of a repetitive transmission scheme, it is less probablethat a UE misses a synchronization signal. Instead, the UE is unable tograsp its location.

FIG. 5 shows an example of a frame structure proposed in a communicationenvironment that uses mmWave.

First of all, a single frame is configured with Q subframes, and asingle subframe is configured with P slots. And, one slot is configuredwith T OFDM symbols. Here, unlike other subframes, a first subframe in aframe uses 0^(th) slot (slot denoted by ‘S’) for the usage ofsynchronization. And, the 0^(th) slot is configured with A OFDM symbolsfor timing and frequency synchronization, B OFDM symbols for beamscanning, and C OFDM symbols for informing a UE of system information.And, the remaining D OFDM symbols are used for data transmission to eachUE.

Meanwhile, such a frame structure is a simple example only. Q, P, T, S,A, B, C and D are random values, and may include values set by a user orvalues set automatically on a system.

In the following, algorithm of timing synchronization between a basestation and a UE is described. Let's consider a case that the basestation transmits the same synchronization signal A times in FIG. 5.Based on the synchronization signal transmitted by the base station, theUE performs timing synchronization using the algorithm of Equation 3.

$\begin{matrix}{\hat{n} = {\arg\;{\min\limits_{\overset{\sim}{n}}\frac{{\sum\limits_{i = 0}^{A - 2}{y_{\overset{\sim}{n},i}^{H}y_{\overset{\sim}{n},{i + 1}}}}}{\sum\limits_{i = 0}^{A - 2}{{y_{\overset{\sim}{n},i}^{H}y_{\overset{\sim}{n},{i + 1}}}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

where y_(ñ,i) Δr[ñ+i(N+N_(g)):ñ+i(N+N_(g))+N−1]

In Equation 3, N, N_(g) and i indicate a length of OFDM symbol, a lengthof CP (Cyclic Prefix) and an index of OFDM symbol, respectively. r meansa vector of a received signal in a receiver. Here, the equation y_(ii,i)Δr[ñ+i(N+N_(g)):ñ+i(N+N_(g))+N−1] is a vector defined with elementsranging from (ñ+i(N+N_(g)))th element to (ñ+i(N+N_(g))+N−1)th of thereceived signal vector r.

The algorithm of Equation 3 operates on the condition that 2 OFDMreceived signals adjacent to each other temporally are equal to eachother. Since such an algorithm can use a sliding window scheme, it canbe implemented with low complexity and has a property robust to afrequency offset.

Meanwhile, Equation 4 represents an algorithm of performing timingsynchronization using correlation between a received signal and a signaltransmitted by a base station.

$\begin{matrix}{\hat{n} = {\arg\;{\min\limits_{\overset{\sim}{n}}\frac{{{\sum\limits_{i = 0}^{A - 1}{y_{\overset{\sim}{n},i}^{H}s}}}^{2}}{\sum\limits_{i = 0}^{A - 1}{{y_{\overset{\sim}{n},i}}^{2}{\sum\limits_{i = 0}^{A - 1}{s}^{2}}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In Equation 4, s means a signal transmitted by a base station and is asignal vector pre-agreed between a UE and a base station. Although theway of Equation 4 may have performance better than that of Equation 3,since Equation 4 cannot be implemented by a sliding window scheme, itrequires high complexity. And, the way of Equation 4 has a propertyvulnerable to a frequency offset.

In continuation with the description of the timing synchronizationscheme, a beam scanning process is described as follows. First of all, abeam scanning means an operation of a transmitter and/or a receiver thatlooks for a direction of a beam that maximizes a received SINR of thereceiver. For example, a base station determines a direction of a beamthrough a beam scanning before transmitting data to a UE.

Further description is made by taking FIG. 4 as one example. FIG. 4shows that a sector serviced by a single base station is divided into 8areas. Here, the base station transmits a beam to each of (A1+B1),(A2+B2), (A3+B3) and (A4+B4) areas, and a UE can identify the beamstransmitted by the base station. On this condition, a beam scanningprocess can be embodied into 4 kinds of processes. First of all, thebase station transmits beams to 4 areas in sequence [i]. The UEdetermines a beam decided as a most appropriate beam among the beams inaspect of a received SINR [ii]. The UE feds back information on theselected beam to the base station [iii]. The base station transmits datausing a beam having the direction of the feedback [iv]. Through theabove beam scanning process, the UE can receive DL data through a beamhaving an optimized received SINR.

Zadoff-Chu sequence is described in the following. Zadoff-Chu sequenceis called Chu sequence or ZC sequence and defined as Equation 5.

$\begin{matrix}{{x_{r}\lbrack n\rbrack} = e^{\frac{j\;\pi\; r\;{n{({n + 1})}}}{N}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In Equation 5, N indicates a length of sequence, r indicates a rootvalue, and x_(r)[n] indicates an n^(th) element of ZC sequence. The ZCsequence is characterized in that all elements are equal to each otherin size [constant amplitude]. Moreover, a DFT result of ZC sequence isalso identical for all elements.

In the following, ZC sequence and a cyclic shifted version of the ZCsequence have the following correlation such as Equation 6.

$\begin{matrix}{{\left( x_{r}^{(i)} \right)^{H}x_{r}^{(j)}} = \left\{ \begin{matrix}N & {{{for}\mspace{14mu} i} = j} \\0 & {elsewhere}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In Equation 6, X_(r) ^((i)) is a sequence resulting from cyclic-shiftingX_(r) by i, and indicates 0 except a case that auto-correlation of ZCsequence is i=j. The ZC sequence also has zero auto-correlation propertyand may be expressed as having CAZAC (Constant Amplitude Zero AutoCorrelation) property.

Regarding the final property of the ZC sequence ZC, the correlationshown in Equation 7 is established between ZC sequences having a rootvalue that is a coprime of a sequence length N.

$\begin{matrix}{{x_{r_{1}}^{H}x_{r_{2}}} = \left\{ \begin{matrix}N & {{{for}\mspace{14mu} r_{1}} = r_{2}} \\\frac{1}{\sqrt{N}} & {elsewhere}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

In equation 7, r₁ or r₂ is a coprime of N. For example, if N=111,2≤r₁,r₂≤110 always meets Equation 7. Unlike auto-correlation of Equation6, the mutual correlation of ZC sequence does not become 0 completely.

In continuation with ZC sequence, Hadamard matrix is described. TheHadamard matrix is defined as Equation 8.

$\begin{matrix}{{H_{2^{k}} = {\begin{bmatrix}H_{2^{k - 1}} & H_{2^{k - 1}} \\H_{2^{k - 1}} & {- H_{2^{k - 1}}}\end{bmatrix} = {H_{2} \otimes H_{2^{k - 1}}}}}{{{where}\mspace{14mu} H_{1}} = \lbrack 1\rbrack}{H_{2} = \begin{bmatrix}1 & 1 \\1 & {- 1}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

In Equation 8, 2^(k) indicates a size of matrix. Hadamard matrix is aunitary matrix that always meets H_(n)H_(n) ^(T)=nI_(n) irrespective ofa size n. Moreover, in Hadamard matrix, all columns and all rows areorthogonal to each other. For example, if n=4, Hadamard matrix isdefined as Equation 9.

$\begin{matrix}{H_{4} = \begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

From Equation 9, it can be observed that columns and rows are orthogonalto each other.

FIG. 6 shows a structure of OVSF (orthogonal variable spreading factor)code. The OVSF code is the code generated on the basis of Hadamardmatrix and has specific rules.

First of all, in diverging to the right in the OVSF code [lower branch],a first code repeats a left mother code twice as it is and a second codeis generated from repeating an upper code once, inverting it and thenrepeating the inverted code once. FIG. 6 shows a tree structure of OVSFcode.

Such an OVSF code secures all orthogonality except the relation betweenadjacent mother and child codes on a code tree. For example, in FIG. 6,a code [1 −1 1 −1] is orthogonal to all of [1 1], [1 1 1 1], and [1 1 −1−1]. Moreover, regarding the OVSF code, a length of code is equal to thenumber of available codes. Namely, it can be observed from FIG. 6 that alength of a specific ode is equal to the total number in a branch havingthe corresponding code belong thereto.

FIG. 7 is a diagram to describe a disposed situation of user equipments.RACH (Random Access CHannel) is described with reference to FIG. 7.

In case of LTE system, when RACH signals transmitted by UEs arrive at abase station, powers of the RACH signals of UEs received by the basestation should be equal to each other. To this end, the base stationdefines a parameter ‘preambleInitialReceivedTargetPower’, therebybroadcasting the parameter to all UEs within a corresponding cellthrough SIB (System Information Block) 2. The UE calculates a pathlossusing a reference signal, and then determines a transmit power of theRACH signal using the calculated pathloss and the parameter‘preambleInitialReceivedTargetPower’ like Equation 10.P_PRACH_Initial=min{P_CMAX,preambleInitialReceivedTargetPower+PL}  [Equation 10]

In Equation 10, P_PRACH_Initial, P_CMAX, and PL indicate a transmitpower of RACH signal, a maximum transmit power of UE, and a pathloss,respectively.

Equation 10 is taken as one example for the following description. Amaximum transmittable power of UE is assumed as 23 dBm, and a RACHreception power of a base station is assumed as −104 dBm. And, a UEdisposed situation is assumed as FIG. 7.

First of all, a UE calculates a pathloss using a receivedsynchronization signal and a beam scanning signal and then determines atransmit power based on the calculation. Table 3 shows a pathloss of UEand a corresponding transmit power.

TABLE 3 Additional Necessary Transmit necessary UEpreambleInitialReceivedTargetPower Pathloss transmit power power powerK1 −104 dBm  60 dB −44 dBm  −44 dBm  0 dBm K2 −104 dBm 110 dB  6 dBm  6dBm 0 dBm K3 −104 dBm 130 dB 26 dBm 23 dBm 3 dBm

In case of a UE K1 in table 3, a pathloss is very small. Yet, in orderto match an RACH reception power, an RACH signal should be transmittedwith very small power (−44 dBm). Meanwhile, in case of a UE K2, althougha pathloss is big, a necessary transmit power is 6 dBm. Yet, in case ofa UE K3, since a pathloss is very big, a necessary transmit powerexceeds P_CMA=23 dBm. In this case, the UE should perform a transmissionwith 23 dBm that is a maximum transmit power and a rate of UE's RACHaccess success is degraded by 3 dB.

2. First Proposed Random Access Performing Method

In the following description, a random access procedure (or, an RACHprocedure) performed in a wireless communication system using anultrahigh frequency band is proposed and proposed embodiments aredescribed in detail through FIGS. 8 to 10.

According to a proposed embodiment, in order to lower probability ofcollision occurring in an RACH procedure, a repeatedly transmitted RACHsignal is defined using a sequence and a phase pattern vector. Inparticular, if a user equipment (hereinafter abbreviated UE) repeatedlysends an RACH signal to a base station (hereinafter abbreviated BS) asmany times as a predetermined repetition count, a scalar value appliedto a sequence can be varied instead of repeatedly sending the samesequence simply. Since such a scalar value changes a phase of asequence, it is defined as ‘phase pattern vector’. And, a plurality ofphase pattern vectors can be defined as a single phase pattern vectorset.

For example, although two UEs send RACH signals by selecting a samesequence in an RACH procedure, if the two UEs select different phasepattern vectors, respectively, the RACH procedure can be performedbetween the two UEs without collision. This means that a BS candistinguish the RACH signals of the two UEs without mutual interference.A proposed embodiment is described in detail as follows.

First of all, a phase pattern vector set for an RACH procedure is sharedbetween a UE and a BS. The phase pattern vector set may be shared by theUE and the BS in a manner of being determined by the BS and thentransmitted to the UE. On the other hand, if a fixed phase patternvector set is defined, the UE and the BS agree to use a single phasepattern vector set offline in advance.

Meanwhile, a phase pattern vector set is configured with a plurality ofphase pattern vectors orthogonal or quasi-orthogonal to each other forthe same repetition count. For example, a phase pattern vector setaccording to one embodiment can be implemented in Hadamard form, andeach row or column of the Hadamard matrix described in Equation 8 orEquation 9 can configure a single phase pattern vector. In Table 4, anexample of a phase pattern vector set implemented in Hadamard form isshown. In Table 4, when a vector size is 4, 4 vectors orthogonal to eachother become 4 phase pattern vectors configuring a phase pattern vectorset.

TABLE 4 Index Phase pattern vector 0 [1 1 1 1] 1 [1 −1 1 −1] 2 [1 1 −1−1] 3 [1 −1 −1 1]

According to another embodiment, a phase pattern vector set can beimplemented in DFT (Discrete Fourier Transform) form. Table 5 shows anexample of a phase pattern vector set implemented in DFT form.

TABLE 5 Index Phase pattern vector 0 [1 1 1 1] 1 [1 −1 1 −1] 2 [1 −j −1j] 3 [1 j −1 −j]

Subsequently, using the aforementioned phase pattern vector set, aprocess for a UE to generate an RACH signal is described. A UE selects aprescribed phase pattern vector from a phase pattern vector set andapplies the selected phase pattern vector to a process for transmittingRACH signal as many times as a prescribed repetition count.Particularly, the UE sends RACH signals corresponding to a repetitioncount by multiplying the same sequence by scalar values contained in theselected phase pattern vector.

For example, a repetition count is 4, S₂ is selected as a sequence ofRACH signals, and a 3^(rd) phase pattern vector [1 −1 −1 1] is selectedfrom the phase pattern vector set of Table 4. Such a case is describedas follows. A UE can generate RACH signals to send for the repetitioncount ‘4’ like Equation 11 by applying the selected phase pattern vectorto the selected sequence.S ₂ →−S ₂ →−S ₂ →S ₂  [Equation 11]

According to Equation 11, a UE sends total 4 RACH signals, which aregenerated by applying the phase pattern vector [1 −1 −1 1] to thesequence S₂, for 4 time intervals (e.g., OFDM symbols) to a BS. Eachelement of the phase pattern vector becomes a scalar value by which thesequence is multiplied according to the former description.

Subsequently, a process for a BS to process an RACH signal received froma UE is described. The BS calculates correlation between parameters ofthe received RACH signal and a combination of a random sequence and aphase pattern vector and selects a combination of a specific sequenceand a phase pattern vector, which maximizes a value of the calculatedcorrelation. The BS determines the selected sequence and phase patternvector as a sequence and phase pattern vector used for an RACH procedureby the UE.

A process for a BS to calculate correlation can be expressed as Equation12.

$\begin{matrix}{\left\{ {\hat{j},\hat{k}} \right\} = {\underset{\overset{\sim}{j},\overset{\sim}{k}}{\arg\;\max}{{\sum\limits_{i = 0}^{R - 1}\;{\left( x_{i,j} \right)^{*}y_{i}^{H}s_{\overset{\sim}{k}}}}}^{2}}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In Equation 12, ĵ and {circumflex over (k)} indicate a specific phasepattern vector and sequence, which maximize a correlation value,respectively, −{tilde over (j)} and {tilde over (k)} indicate a randomphase pattern vector and sequence, which become calculation targets ofthe correlation value, respectively, R indicates a repetition count of apredetermined RACH signal, and x_(i,j) indicates an i^(th) element of aj^(th) phase pattern vector. Moreover, in Equation 12, in a similarmanner of the definition of Equation 3, y_(i) is a vector defined with[i(N+N_(g))]^(th) to [i(N+N_(g))+N−1]^(th) elements of an Rx signalvector r of a BS, and s_({tilde over (k)}) indicates a

th sequence in the whole sequence set.

Eventually, Equation 12 means a process for a BS to calculatecorrelation values among a received RACH signal, a random sequences_({tilde over (k)}) and a random phase pattern vector {tilde over(j)}([x_(0,{tilde over (j)})x_(1,{tilde over (j)}). . .x_(R-1,{tilde over (j)})]). The BS searches for a sequence and phasepattern vector combination ({circumflex over (k)},ĵ) that maximizes acorrelation value ({circumflex over (k)},ĵ).

For example, Table 6 shows sequences and phase pattern vectors selectedby 3 user equipments UE 1, UE 2, and UE 3. Here, a repetitivetransmission count of RACH signal is 4 and a phase pattern vector set ofTable 4 is used. Such a case is represented.

TABLE 6 UE Sequence Phase pattern vector UE 1 S₀ [1 1 −1 −1] (Index 2)UE 2 S₀ [1 −1 −1 1] (Index 3) UE 3 S₁ [1 −1 −1 1] (Index 3)

In Table 6, let's consider a case that 3 UEs send RACH signalsrepeatedly 4 times through the same time and frequency resources. Inthis case, a BS calculates correlation values of RACH signals receivedfrom the respective UEs through Equation 12, and a correlation valuecalculating process of the BS is described with reference to FIG. 8. InFIG. 8, α_(i,k) is defined as α_(i,k) Δy_(i) ^(H)s_(k). α_(i,k) ^(u) isdefined as α_(i,k) ^(u) Δy_(i,u) ^(H)s_(k). And, y_(i,u) ^(H) indicatesan Rx signal of a BS when a uth UE sends an RACH signal but the rest ofUEs fail to send RACH signals. If a channel is flat, does not changeaccording to time, and has no noise, such relation as x_(0,j)*α_(0,k)^(u)= . . . =x_(R-1,j)*α_(R-1,k) ^(u)=α_(k) ^(u) is established. Forclarity of the description, if such a channel state is assumed,correlation values calculated by a BS can be illustrated as FIG. 8.

In FIG. 8, it can be observed that an RACH signal (sequence index 0,phase pattern vector index 2) sent by UE 1 is detected from a 3^(rd)correlation value. And, it can be observed that an RACH signal (sequenceindex 0, phase pattern vector index 3) sent by UE 2 is detected from a4^(th) correlation value in FIG. 8. Moreover, it can be observed that anRACH signal (sequence index 1, phase pattern vector index 3) sent by UE3 is detected from an 8^(th) correlation value in FIG. 8.

Particularly, despite that UE 1 and UE 2 selected the same sequence, asa result from applying different phase pattern vectors, a BS candistinguish RACH signals of the two UEs. Therefore, the BS candistinguish RACH signals in case of different phase pattern vectorindexes as well as RACH signals in case of different sequences.

Meanwhile, it can be observed from FIG. 8 that 4 correlation valuescorresponding to the sequence index 0 can be represented as acombination of 4 scalar values {α_(0,0), α_(1,0), α_(2,0), α_(3,0)}.Namely, the BS can easily obtain 4 correlation values in a manner ofperforming calculation on 4 scalar values and then applying a phasepattern vector to the scalar values. Here, since a steps of applying thephase pattern vector is a simple sign change only whereas calculation ofα_(i,k) Δy_(i) ^(H)s_(k) is a product operation of a vector and avector, complexity due to the application of the phase pattern vector isrelatively insignificant.

Meanwhile, if the BS identifies the RACH signal sent by the UE in theabove manner, the BS sends an RACH response signal indicating anestimated sequence and phase pattern vector to the UE. Here, thesequence and phase pattern vector indexes estimated by the BS may berepresented as RA-PID (random access preamble ID). If phase patternvector indexes are different despite the same sequence, a differentRA-PID is generated. The BS sends the RA-PID to the UE in a manner thatthe RA-PID is contained in the RACH response signal.

In this case, the RA-PID should be defined to express both a sequenceindex and a phase pattern vector index. For example, if a sequence indexis 64 and a phase pattern vector index is 1, RA-PID can be expressed asEquation 13.

$\begin{matrix}{\underset{\underset{64}{︸}}{111110}\underset{\underset{1}{︸}}{01}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

The BS generates and sends an RA-PID contained RACH response signal tothe UE, thereby informing the UE that the RACH signal of the UE wasreceived.

FIG. 9 is a flowchart showing a method of performing a random accessprocedure according to one embodiment. FIG. 9 shows the aforementionedembodiments according to a time-series flow. Hence, the above-proposedembodiments are applicable identically or similarly despite that thedetails are omitted from the description with reference to FIG. 9.

First of all, in S910, a sequence set and a phase pattern vector set foran RACH signal transmission are shared between a BS and a UE. What kindsof a sequence set and a phase pattern vector set will be used for anRACH procedure can be determined and then notified to the UE by the BS.Or, a specific sequence set and a specific phase pattern vector set maybe shared beforehand between the UE and the BS in form of agreement.

The UE selects a sequence and phase pattern vector to use for the RACHprocedure according to an RACH signal repetitive transmission count[S9920]. A step of determining the repetitive transmission count of theRACH signal shall be described in detail with reference to FIG. 10. Forexample, if a repetitive transmission count is 4, a prescribed phasepattern vector is selected from a phase pattern vector set correspondingto ‘4’ and a prescribed sequence is selected from a sequence set.

Subsequently, the UE sends an RACH signal generated from applying theselected sequence and phase pattern vector to the BS [S930]. The RACHsignal sent by the UE is sent to the BS for a time interval amounting toa predetermined repetition count, and may be generated from multiplyingthe sequence selected in S920 by elements of the phase pattern vectorselected in S920.

Meanwhile, the BS estimates a sequence and phase pattern vector of theRACH signal sent by the UE [S940]. Namely, the BS calculates a sequenceand phase pattern vector applied to the transmission of the RACH signalby the UE through a step of calculating a correlation value between thereceived RACH signal and a combination of a random sequence and phasepattern vector. Such a step may be understood as a step of selecting asequence and phase pattern vector, which maximize a correlation valueaccording to Equation 12.

Subsequently, the BS sends an RACH response signal, which indicates thesequence and phase pattern vector estimated as used by the UE, to the UE[S950]. The RACH response signal may be sent in a manner of containingRA-PID indicating the estimated sequence and phase pattern vector.Having received the RACH response signal, the UE checks whether thesequence and phase pattern vector estimated by the BS match the sequenceand phase pattern vector applied to the RACH signal by the UE itself,thereby checking whether the RACH procedure is successfully performed[S960].

According to the above-proposed embodiments, although UEs perform anRACH procedure by selecting a same sequence, if phase pattern vectorsare different, a BS can distinguish them without interference. By simplyincreasing the number of sequences, it is able to resolve the collisionof the RACH procedure between UEs. Yet, if the number of the sequencesis increased, the following problems are caused. First of all, thehigher the number of sequences gets, the larger inter-sequencecorrelation becomes. Hence, inter-sequence interference increases. Ifthe sequence interference increases, it may cause a problem of degradingBS's sequence estimation performance Secondly, in LTE/LTE-A, a UE isinformed of a sequence, which is usable for each cell, through SIB(system information block). If the number of sequences is increased,signaling information of such an SIB should be modified. Hence, it maycause a problem in aspect of backward compatibility. Moreover, in orderto minimize RACH signal interference between cells, it may cause aproblem that a predefined sequence table should be modified all. Inorder to support a legacy UE, it may cause a problem that an existingsequence table should be retained as well.

On the contrary, according to a proposed embodiment, a new phase patternvector is introduced additionally while an existing sequence set isutilized intactly. By utilizing a sequence and phase pattern vector, thenumber of RACH signals selectable by a UE becomes (size of sequence setX size of phase pattern vector set). As the number of RACH signalsincreases, complexity of BS's estimation step rises. Yet, since a phasepattern vector calculating step is a simple scalar operation step only,as described above, it is advantageous in that the complexity rise isrelatively negligible.

FIG. 10 is a flowchart showing a repetition count determining methodaccording to another proposed embodiment. With respect to the formerproposed embodiment, a process for determining a repetitive transmissioncount of RACH signals is described with reference to FIG. 10.

First of all, a BS sends a default repetition count and a maximumrepetition count for transmission of RACH signal to a UE [S1010]. Thedefault repetition count or the maximum repetition count is selected asa repetition count the UE will apply to the transmission of the RACHsignal actually.

Meanwhile, the UE calculates a pathloss through a synchronizationprocedure and a beam scanning procedure performed ahead of an RACHprocedure [S1020]. Subsequently, the UE determines RACH Rx power of theBS and RACH Tx power of the UE based on the calculated pathloss [S1030].Here, the RACH Rx power means an Rx power estimated when an RACH signalsent by the UE arrives at the BS. And, the UE determines RACH Tx powerof its own to match the RACH Rx power. Such steps are already describedin FIG. 7 and Equation 10, and the corresponding details shall beomitted.

Subsequently, the UE compares the determined RACH Tx power with themaximum Tx power of the UE [S1030], thereby determining a finalrepetition count [S1040]. If the determined RACH Tx power is smallerthan the maximum Tx power of the UE, the UE determines the defaultrepetition count received in S1010 as an RACH repetitive transmissioncount. If the determined RACH Tx power is greater than the maximum Txpower of the UE, the UE determines the maximum repetition count receivedin S1010 as an RACH repetitive transmission count. In the latter case,the UE may determine a random count smaller than the maximum repetitioncount as an RACH repetition count using a difference or ratio betweenthe RACH Tx power and the maximum Tx power of the UE.

The following description is made by taking a case that a defaultrepetition count and a maximum repetition count are 4 and 16,respectively as an example. First of all, a UE calculates a pathloss anddetermines RACH Tx power of the UE from RACH Rx power of a BS. If Table3 is taken as one example, in case of a UE K1 and a UE L2, since anecessary Tx power is smaller than UE's maximum Tx power (23 dB), anRACH repetition count becomes 4. Meanwhile, in case of a UE K3, since anecessary Tx power is greater than a maximum Tx power by a size of 3 dB,the RACH success rate of the UE is degraded by the size. In this case,the UE determines a repetition count not as 4 but as a maximum repletioncount ‘16’. If so, the UE K3 can obtain an additional power gain of 6 dBand an RACH success rate enhanced better than those of other UEs. Or,based on a difference or ratio between a necessary Tx power and amaximum Tx power, the UE K3 may determine a repetition count as ‘8’smaller than the maximum repetition count.

3. Second Proposed Random Access Performing Method

In the above description, described is an embodiment of utilizing asequence and a phase pattern vector in an RACH procedure between a UEand a BS. In the following, described is an embodiment of adaptivelyadjusting a transmission timing of an RACH signal in addition to theaforementioned RACH procedure. According to embodiments described below,as a transmission timing of an RACH signal sent by a UE is adjusted,although RSCH signals using the same phase pattern vector for the samerepetition count are sent, a BS can distinguish them.

FIG. 11 is a diagram to describe a method of performing a random accessprocedure according to another embodiment. Regarding FIG. 11, thefollowing description is made by taking an example of a case that adefault repetition count and a maximum repetition count are determinedas 4 and 8, respectively.

In case that a default repetition count and a maximum repetition countare determined as 4 and 8, respectively, a UE can send RACH signals in0^(th) and 4^(th) OFDM symbols among 0^(th) to 7^(th) OFDM symbols.Referring to FIG. 11, a UE A sends an RACH signal in the 0^(th) OFDMsymbol, and a UE B sends an RACH signal in the 4^(th) ODFM symbol.Meanwhile, if a repetition count of a UE is determined as 8 equal to amaximum repetition count, the UE should send an RACH signal by startingwith the 0^(th) OFDM symbol. Such an example is summarized andrepresented in Table 7.

TABLE 7 Repetition count Transmittable timing 4 0, 4 8 0

In FIG. 11, since the RACH signals sent by the UE A and the UE B aresent at different timings, respectively, a BS can detect the RACHsignals of the two UEs by avoiding the overlapping between the RACHsignals. Namely, as the two RACH signals are detected, the BS can beaware that the two UEs are attempting access, which is the same as thecase that the UE A and the UE B use the same sequence and the same phasepattern vector. In response to this, the BS generates 2 RACH responsesignals indicating 2 different transmission timings and then sends themto the UEs, respectively.

The UE acquires information on an RA-PID (i.e., sequence and phasepattern vector) and a transmission timing, which are estimated by theBS, through the RACH response signal, and then compares the informationwith RA-PID and transmission timing of the RACH signal sent by the UE.If a comparison result says ‘identical’, the UE determines that its RACHprocedure has been performed successfully. Yet, as a result of thecomparison, if at least one of the sequence, the phase pattern vector,and the transmission timing is not matched, the RACH procedure on the BSis determined as failure. Eventually, the UE A and the UE B can performRach procedure on the BS by sending RACH signals at a specific timing inthe whole transmission interval corresponding to a maximum repetitioncount. So to speak, according to the proposed embodiment, byinformationalizing a transmission timing of an RACH signal, RACHcollision probability can be further reduced.

Meanwhile, in the aforementioned process, the BS can inform UEs of aphase pattern vector set usable at a specific repetition count. Here, ina step of sharing a phase pattern vector set between a UE and a BS likeS910 of FIG. 9, the BS may inform the UE of some phase pattern vectorsusable or unusable for each repetition count within the phase patternvector set. Moreover, phase pattern vectors having different repetitioncounts may be set to lie in mutually nested orthogonal relation.

For a detailed example, in a phase pattern vector set for a repetitioncount 4 represented in Table 8, a phase pattern vector of an index #3 isset as an unusable phase pattern vector. Table 9 shows a case that aphase pattern vector of an index #3 and a phase pattern vector of anindex #7 in a phase pattern vector set for a repetition count 8 are setas usable phase pattern vectors only. Meanwhile, phase pattern vectorsrepresented in Table 8 and Table 9 are defined on the basis of OVSF(orthogonal variable spreading factor) codes.

TABLE 8 Index Phase pattern vector Usable/Unusable 0 [1 1 1 1] Usable 1[1 1 −1 −1] Usable 2 [1 −1 1 −1] Usable 3 [1 −1 −1 1] Unusable

TABLE 9 Index Phase pattern vector Usable/Unusable 0 [1 1 1 1 1 1 1 1]Unusable 1 [1 1 −1 −1 1 1 −1 −1] Unusable 2 [1 −1 1 −1 1 −1 1 −1]Unusable 3 [1 −1 −1 1 1 −1 −1 1] Usable 4 [1 1 1 1 −1 −1 −1 −1] Unusable5 [1 1 −1 −1 −1 −1 1 1] Unusable 6 [1 −1 1 −1 −1 1 −1 1] Unusable 7 [1−1 −1 1 −1 1 1 −1] Usable

The reason why some phase pattern vectors are set unusable in such aphase pattern vector set is to satisfy the nested orthogonal propertybetween phase pattern vectors of different repetition counts. Namely,since some of vectors in the phase pattern vector set has not inclusiverelation to vectors of a different repetition count (i.e., not nestedorthogonal), if such vectors are used together with the vector of thedifferent repetition count, the BS is unable to distinguish the two RACHsignals. Hence, the BS may be set to use some vectors, which meet thenested orthogonal property, among the vectors included in the phasepattern vector set only. This is described in detail through theembodiment shown in FIG. 12.

FIG. 12 is a diagram to describe a method of performing a random accessprocedure according to another embodiment. FIG. 12 shows the followingcase. First of all, a UE A performs an RACH procedure using a phasepattern vector of an index 0 in a phase pattern vector set having arepetition count ‘4’ in Table 8, a UE B performs an RACH procedure usinga phase pattern vector of an index 2 in Table 8, a UE C performs an RACHprocedure using a phase pattern vector of an index 2 in Table 8, and aUE D performs an RACH procedure using a phase pattern vector of an index3 in Table 8. Each of the UE A and the UE B sends an RACH signal at a0^(th) timing, the UE C sends an RACH signal at a 4th timing, and the UED sends an RACH signal at a 0^(th) timing. Each of the UEs A to C has arepetition count ‘4’, and the UE D has a repetition count ‘8’.

The BS processes the received 4 RACH signals according to Equation 14.

$\begin{matrix}{\left\{ {\hat{j},\hat{R},\hat{k}} \right\} = {\underset{\overset{\sim}{j},\overset{\sim}{R},\overset{\sim}{k}}{\arg\;\max}{{\sum\limits_{i = 0}^{\overset{\sim}{R} - 1}{\left( x_{i,\overset{\sim}{j}}^{\overset{\sim}{R}} \right)^{*}y_{i}^{H}s_{\overset{\sim}{k}}}}}^{2}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

Parameters of Equation 14 are identical to those of Equation 12, x_(i,j)^(R) indicates an i^(th) element of a j^(th) phase pattern vector of arepetition count R, and {circumflex over (R)} indicates a repetitioncount that makes a correlation value become a maximum. For example,0^(th) and 1^(st) elements of a 3^(rd) phase pattern vector (index=3) ina phase pattern vector set of a repetition count ‘8’ are 1 and −1,respectively. The BS searches for {ĵ, {circumflex over (R)}, {tilde over(k)}} that makes a correlation value become a maximum through Equation14.

Meanwhile, since the UE A and the UE B select different phase patternvectors in FIG. 12 and the two phase pattern vectors are orthogonal toeach other, the BS can distinguish RACH signals of the two UEs. Sincethe UE C and the UE A/B differ from each other in a transmission timing,the RACH signal of the UE C is received at a transmission timingdifferent from those of the RACH signals of the UEs A and B. Hence, theBS can distinguish the RACH signal of the UE C as well.

The case of the UE D and the UE A/B/C is described with reference toTable 10 as follows. In Table 10, [0 0 0 0] indicates that thecorresponding UE does not sent an RACH signal at the correspondingtiming.

TABLE 10 Phase pattern vector Phase pattern vector UE (transmissiontiming 0) (transmission timing 4) A [1 1 1 1] [0 0 0 0] B [1 −1 1 −1] [00 0 0] C [0 0 0 0] [1 −1 1 −1] D [1 −1 −1 1] [1 −1 −1 1]

If an estimated repetition count is 4, Table 10 shows that phase patternvectors are always orthogonal to each other irrespective of atransmission timing. When the BS identifies the RACH signal of the UE A,since the RACH signal of the UE D has an orthogonal phase patternvector, it does not cause interference. Likewise, Since phase patternvectors are orthogonal to each other between the RACH signals of the UEsC and D, interference is not caused. Meanwhile, the BS detects [1 −1 −11] vector of the UE D at each of the transmission timing 0 and thetransmission timing 4. Yet, since the phase pattern vector [1 −1 −1 1]of the index 3 is set unusable in Table 8, the BS can recognize that the[1 −1 −1 1] vector is not the phase pattern vector of the repetitioncount 4 but the phase pattern vector having the index 3 of therepetition count 8 in Table 9.

Subsequently, if the estimated repetition count is 8 in Table 10, the BScalculates correlation by applying 3^(rd) and 7^(th) phase patternvectors of Table 9. In this case, each of the phase pattern vectors ofthe UEs A, B and C is orthogonal to the phase pattern vector of the UED. The following description is made by taking the UE C as an example.As a vector [0 0 0 0 1 −1 1 −1] generated from adding [0 0 0 0] to thephase pattern vector of the UE C is orthogonal to the phase patternvector of the UE D for the transmission timing 0, the phase patternvectors of the UE C and the UE D are nested orthogonal to each other.This identically applies between the UE A/B and the UE D. Eventually,when the UE D is identified, RACH signals of the rest of the UEs have noeffect. As described above, this is because some phase pattern vectorsusable for each repetition count are set in advance.

When a usable or unusable phase pattern vector is set per repetitioncount in advance, as described above, the BS can identify RACH signalsbetween UEs having different repetition counts without interference.This means that the BS can identify an RACH signal irrespective of aspecific timing for a random UE to send the RACH signal in a wholetransmission interval.

Meanwhile, although a usable or unusable phase pattern vector perrepetition count may be shared between a BS and a UE in a manner ofbeing notified to the UE by the BS, a phase pattern vector set fixed inoffline form may be determined between the UE and the BS in advance.

According to another embodiment, a size of a phase pattern vector foreach repetition count can be adjusted differently depending on a serviceradius of a cell. If the service radius (or, size) of the cellincreases, a size of a phase pattern vector set having a big repetitioncount is defined lager and a size of a phase pattern vector set having asmall repetition count is defined small. On the contrary, if the serviceradius (or, size) of the cell is small, a size of a phase pattern vectorset having a big repetition count is defined small and a size of a phasepattern vector set having a small repetition count is defined large. Ifa size of a phase pattern vector is large/small, it means that thenumber of usable phase pattern vectors included in the corresponding setis big/small.

If the BS services an area C1 only in FIG. 7, the repetition count ofRACH signal selected by most of UEs may be small. On the contrary, ifthe BS services up to an area C3, many UEs may desire a biggerrepetition count of RACH signal. In the latter case, if a size of aphase pattern vector set having a high repetition count is set small(i.e., less phase pattern vectors included in the phase pattern vectorset of the high repetition count are set), probability for UEs to selecta same phase pattern vector is raised. Hence, probability of RACH signalcollision between UEs increases as well. Therefore, the BS sets moreusable phase pattern vectors included in a phase pattern vector sethaving a high repetition count but may set less usable phase patternvectors included in a phase pattern vector set of a relatively smallrepetition count.

For example, if the BS services the area C1 only, phase pattern vectorsets of repetition counts 4 and 8 may be determined as Table 11 andTable 12, respectively.

TABLE 11 Index Phase pattern vector Usable/unusable 0 [1 1 1 1] Usable 1[1 1 −1 −1] Unusable 2 [1 −1 1 −1] Usable 3 [1 −1 −1 1] Unusable

TABLE 12 Index Phase pattern vector Usable/unusable 0 [1 1 1 1 1 1 1 1]Unusable 1 [1 1 −1 −1 1 1 −1 −1] Usable 2 [1 −1 1 −1 1 −1 1 −1] Unusable3 [1 −1 −1 1 1 −1 −1 1] Usable 4 [−1 −1 −1 −1 −1 −1 −1 −1] Unusable 5 [11 −1 −1 −1 −1 1 1] Usable 6 [1 −1 1 −1 −1 1 −1 1] Unusable 7 [1 −1 −1 1−1 1 1 −1] Usable

Compared with Table 8 and Table 9, size changes of phase pattern vectorsets of Table 11 and Table 12 are shown in Table 13.

TABLE 13 Repetition # of usable vectors # of usable vectors count beforeadjustment after adjustment 4 3 2 8 2 4

According to Table 13, the number of usable vectors is reduced into 2from 3 in the phase pattern vector set of a repetition count 4. Yet, thenumber of usable vectors is raised to 4 from 2 in the phase patternvector set of a repetition count 8.

Meanwhile, configurations such as Table 11 and Table 2 are not uniqueembodiments but simple examples. Namely, a phase pattern vector of anindex 2 can be configured as unusable instead of an index 1 in Table 11.In this case, phase pattern vectors of indexes 2 and 6 become usableinstead of phase pattern vectors of indexes 1 and 5 in Table 12.

FIG. 13 is a flowchart showing a method of performing a random accessprocedure according to further proposed embodiment. FIG. 13 shows theaforementioned embodiments according to a time-series flow. Hence, theabove-proposed embodiments are applicable identically or similarlydespite that the details are omitted from the description with referenceto FIG. 13.

First of all, in S1310, a sequence set and a phase pattern vector setfor an RACH signal transmission are shared between a BS and a UE. Here,a phase pattern vector set for a random repetition count may beconfigured with usable phase pattern vectors only among phase patternvectors orthogonal to each other. So to speak, the phase pattern vectorset of S1310 may mean phase pattern vectors except an unusable phasepattern vector set among all phase pattern vectors for a specificrepetition count.

Meanwhile, what kinds of a sequence set and a phase pattern vector setwill be used for an RACH procedure can be determined and then notifiedto the UE by the BS. Or, a specific sequence set and a specific phasepattern vector set may be shared beforehand between the UE and the BS inform of agreement.

Subsequently, the UE selects a sequence and phase pattern vector to usefor the RACH procedure according to an RACH signal repetitivetransmission count [S1320]. The step described with reference to FIG. 10may be similarly applicable to a step of determining the repetitivetransmission count of the RACH signal. For example, if a repetitivetransmission count is 4, a prescribed phase pattern vector is selectedfrom usable phase pattern vectors included in a phase pattern vector setcorresponding to ‘4’ and a prescribed sequence is selected from asequence set.

Subsequently, the UE sends an RACH signal generated from applying theselected sequence and phase pattern vector to the BS, and the RACHsignal is sent at a specific timing in a whole transmittable interval(i.e., a time interval corresponding to a maximum repetition count)[S1330]. The RACH signal sent by the UE is sent to the BS for a timeinterval amounting to a predetermined repetition count, and may begenerated from multiplying the sequence selected in S1320 by elements ofthe phase pattern vector selected in S1320.

The BS estimates a sequence, phase pattern vector and repetition countof the RACH signal sent by the UE [S1340]. Namely, the BS calculates asequence, phase pattern vector and repetition count applied to thetransmission of the RACH signal by the UE through a step of calculatinga correlation value between the received RACH signal and a combinationof a random sequence, phase pattern vector and repetition count. Such astep may be understood as a step of selecting a sequence, phase patternvector and repetition count, which maximize a correlation valueaccording to Equation 14.

Subsequently, the BS sends an RACH response signal, which indicates thesequence, phase pattern vector and transmission timing estimated as usedby the UE, to the UE [S1350]. The RACH response signal may be sent in amanner of containing RA-PID indicating the estimated sequence and phasepattern vector. Having received the RACH response signal, the UE checkswhether the sequence, phase pattern vector and repetition countestimated by the BS match the parameters and transmission timing appliedto the RACH signal by the UE itself, thereby checking whether the RACHprocedure is successfully performed [S1360].

According to the above-proposed embodiments, although UEs perform anRACH procedure by selecting a same sequence and a same phase patternvector, if transmission timings are different, a BS can distinguish themwithout interference.

4. Apparatus Configuration

FIG. 14 is a block diagram showing the configuration of a user equipmentand a base station according to one embodiment of the present invention.In FIG. 11, the user equipment 100 and the base station 200 may includeradio frequency (RF) units 110 and 210, processors 120 and 220 andmemories 130 and 230, respectively. Although a 1:1 communicationenvironment between the user equipment 100 and the base station 200 isshown in FIG. 11, a communication environment may be established betweena plurality of user equipment and the base station. In addition, thebase station 200 shown in FIG. 11 is applicable to a macro cell basestation and a small cell base station.

The RF units 110 and 210 may include transmitters 112 and 212 andreceivers 114 and 214, respectively. The transmitter 112 and thereceiver 114 of the user equipment 100 are configured to transmit andreceive signals to and from the base station 200 and other userequipments and the processor 120 is functionally connected to thetransmitter 112 and the receiver 114 to control a process of, at thetransmitter 112 and the receiver 114, transmitting and receiving signalsto and from other apparatuses. The processor 120 processes a signal tobe transmitted, sends the processed signal to the transmitter 112 andprocesses a signal received by the receiver 114.

If necessary, the processor 120 may store information included in anexchanged message in the memory 130. By this structure, the userequipment 100 may perform the methods of the various embodiments of thepresent invention.

The transmitter 212 and the receiver 214 of the base station 200 areconfigured to transmit and receive signals to and from another basestation and user equipments and the processor 220 are functionallyconnected to the transmitter 212 and the receiver 214 to control aprocess of, at the transmitter 212 and the receiver 214, transmittingand receiving signals to and from other apparatuses. The processor 220processes a signal to be transmitted, sends the processed signal to thetransmitter 212 and processes a signal received by the receiver 214. Ifnecessary, the processor 220 may store information included in anexchanged message in the memory 230. By this structure, the base station200 may perform the methods of the various embodiments of the presentinvention.

The processors 120 and 220 of the user equipment 100 and the basestation 200 instruct (for example, control, adjust, or manage) theoperations of the user equipment 100 and the base station 200,respectively. The processors 120 and 220 may be connected to thememories 130 and 230 for storing program code and data, respectively.The memories 130 and 230 are respectively connected to the processors120 and 220 so as to store operating systems, applications and generalfiles.

The processors 120 and 220 of the present invention may be calledcontrollers, microcontrollers, microprocessors, microcomputers, etc. Theprocessors 120 and 220 may be implemented by hardware, firmware,software, or a combination thereof.

If the embodiments of the present invention are implemented by hardware,Application Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), etc. may be included in the processors 120 and 220.

Meanwhile, the aforementioned method may be implemented as programsexecutable in computers and executed in general computers that operatethe programs using computer readable media. In addition, data used inthe aforementioned method may be recorded in computer readable recordingmedia through various means. It should be understood that programstorage devices that can be used to describe storage devices includingcomputer code executable to perform various methods of the presentinvention do not include temporary objects such as carrier waves orsignals. The computer readable media include storage media such asmagnetic recording media (e.g. ROM, floppy disk and hard disk) andoptical reading media (e.g. CD-ROM and DVD).

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

INDUSTRIAL APPLICABILITY

The aforementioned random access performing method is applicable tovarious wireless communication systems including an IEEE 802.16x systemand an IEEE 802.11x system as well as to a 3GPP LTE/LTE-A system.Moreover, a proposed method is applicable to an mmWave communicationsystem that uses an ultra-high frequency band.

What is claimed is:
 1. A method of performing a random access by a user equipment (UE) in a wireless communication system, the method comprising: obtaining information on a sequence set and information on a phase pattern vector set among a plurality of phase pattern vector sets, wherein the sequence set and the phase pattern vector set comprise a plurality of sequences and a plurality of phase pattern vectors, respectively; wherein a respective phase pattern vector set among the plurality of phase pattern vector sets is pre-configured differently according to respective repetitive transmission count among a plurality of repetitive transmission counts for a random access channel (RACH) signal; selecting a phase pattern vector from the plurality of phase pattern vectors; selecting a sequence from the plurality of sequences; obtaining the RACH signal based on the sequence and the selected phase pattern vector, wherein a phase of the sequence is changed by applying the selected phase pattern vector to the sequence; transmitting, to a base station (BS), the RACH signal repeatedly for as many times as a repetitive transmission count, included in the plurality of repetitive transmission counts, at a specific transmission timing in a whole time interval related to a maximum repetitive transmission count; and receiving, from the BS, a RACH response signal comprising information on an estimated sequence, information on an estimated phase pattern vector and information on an estimated transmission timing, wherein the specific transmission timing denotes a specific orthogonal frequency division multiplexing (OFDM) symbol with an index, and the index is determined based on the maximum repetitive transmission count.
 2. The method of claim 1, wherein the respective phase pattern vector set comprises usable phase pattern vectors and at least one unusable phase pattern vector, wherein the plurality of usable phase pattern vectors are orthogonal to each other, and wherein the at least one unusable phase pattern vector is not orthogonal to the plurality of usable phase pattern vectors, respectively.
 3. The method of claim 1, wherein in case that: the maximum repetitive transmission count is 8, the specific transmission timing is a 0^(th) OFDM symbol, the maximum repetitive transmission count is 4, the specific transmission timing is one of the 0^(th) OFDM symbol or a 4^(th) OFDM symbol, and the maximum repetitive transmission count is 2, the specific transmission timing is one of the 0^(th) OFDM symbol, a 2^(nd) OFDM symbol, the 4^(th) OFDM symbol, or a 6^(th) OFDM symbol.
 4. The method of claim 1, wherein the estimated sequence, the estimated phase pattern vector and the estimated transmission timing are determined based on a sequence, a phase pattern vector and a repetition count that maximize a correlation value with the RACH signal transmitted by the UE, respectively.
 5. The method of claim 1, wherein in case that a service radius of the BS increases, a number of phase pattern vectors configuring a phase pattern vector set of a big repetition count is defined to increase and a number of phase pattern vectors configuring a phase pattern vector set of a small repetition count is defined to decrease.
 6. The method of claim 1, wherein the respective phase pattern vector set comprises a plurality of usable phase pattern vectors and at least one unusable phase pattern vector, wherein a first usable phase pattern vector included in a first phase pattern vector set for a first specific repetition count is orthogonal to a part of a second usable phase pattern vector included in a second phase pattern vector set for a second specific repetition count which is larger than the first repetition count, wherein a number of elements included in the first usable phase pattern vector is less than a number of elements included in the second usable phase pattern vector.
 7. The method of claim 1, wherein a number of phase pattern vectors included in a first phase pattern vector set, among the plurality of the phase pattern vector sets, for a first specific repetition count is less than a number of phase pattern vectors included in a second phase pattern vector set, among the plurality of the phase pattern vector sets, for a second specific repetition count which is larger than the first repetition count.
 8. A user equipment (UE) for performing a random access in a wireless communication system, the UE comprising: a transmitter; a receiver; and at least one processor coupled with the transmitter and the receiver, wherein the at least one processor is configured to: obtain information on a sequence set and information on a phase pattern vector set among a plurality of phase pattern vector sets, wherein the sequence set and the phase pattern vector set comprise a plurality of sequences and a plurality of phase pattern vectors, respectively; wherein a respective phase pattern vector set among the plurality of phase pattern vector sets is pre-configured differently according to respective repetitive transmission count among a plurality of repetitive transmission counts for a random access channel (RACH) signal; select a phase pattern vector from the plurality of phase pattern vectors; select a sequence from the plurality of sequences; obtain the RACH signal based on the sequence and the selected phase pattern vector, wherein a phase of the sequence is changed by applying the selected phase pattern vector to the sequence; transmit, to a base station (BS), the RACH signal repeatedly for as many times as the repetitive transmission count, included in the plurality of repetitive transmission counts, at a specific transmission timing in a whole time interval related to a maximum repetitive transmission count; and receive, from the BS, a RACH response signal comprising information on an estimated sequence, information on an estimated phase pattern vector and information on an estimated transmission timing, wherein the specific transmission timing denotes a specific orthogonal frequency division multiplexing (OFDM) symbol with an index, and the index is determined based on the maximum repetitive transmission count.
 9. The UE of claim 8, wherein the respective phase pattern vector set comprises usable phase pattern vectors and at least one unusable phase pattern vector, wherein the plurality of usable phase pattern vectors are orthogonal to each other, and wherein the at least one unusable phase pattern vector is not orthogonal to the plurality of usable phase pattern vectors, respectively.
 10. The UE of claim 8, wherein in case that: the maximum repetitive transmission count is 8, the specific transmission timing is a 0^(th) OFDM symbol, the maximum repetitive transmission count is 4, the specific transmission timing is one of the 0^(th) OFDM symbol or a 4^(th) OFDM symbol, and the maximum repetitive transmission count is 2, the specific transmission timing is one of the 0^(th) OFDM symbol, a 2^(nd) OFDM symbol, the 4^(th) OFDM symbol, or a 6^(th) OFDM symbol.
 11. The UE of claim 8, wherein the estimated sequence, the estimated phase pattern vector and the estimated transmission timing are determined based on a sequence, a phase pattern vector and a repetition count that maximize a correlation value with the RACH signal transmitted by the UE, respectively.
 12. The UE of claim 8, wherein in case that a service radius of the BS increases, a number of phase pattern vectors configuring a phase pattern vector set of a big repetition count is defined to increase and a number of phase pattern vectors configuring a phase pattern vector set of a small repetition count is defined to decrease.
 13. The UE of claim 8, wherein the respective phase pattern vector set comprises a plurality of usable phase pattern vectors and at least one unusable phase pattern vector, wherein a first usable phase pattern vector included in a first phase pattern vector set for a first specific repetition count is orthogonal to a part of a second usable phase pattern vector included in a second phase pattern vector set for a second specific repetition count which is larger than the first repetition count, wherein a number of elements included in the first usable phase pattern vector is less than a number of elements included in the second usable phase pattern vector.
 14. The UE of claim 8, wherein a number of phase pattern vectors included in a first phase pattern vector set, among the plurality of the phase pattern vector sets, for a first specific repetition count is less than a number of phase pattern vectors included in a second phase pattern vector set, among the plurality of the phase pattern vector sets, for a second specific repetition count which is larger than the first repetition count. 